I think Xeno hit the nail on the head ( oops! I just cracked an unintentional crucifixion joke ) - contemporary writers of the period make no mention of Jesus or his miracles - a bit strange since, if even one of them were true, it would be a thousand times more remarkable than the entire career of Alexander or Caesar (neither of whom claimed to re-animate dead people or cure leprosy), yet no-one at the time considered it worthy of recording?

Since most of the Gospels were written in the second century AD, they were clearly not written by people who actually knew Jesus personally (supposing he even existed). Even the oldest Gospel, attributed to Mark, dates to about 70-90 AD. Considering average life expectancy in classical antiquity was considerably less than in modern developed countries, even the author of the oldest gospel is unlikely to be relating anything other than second or third hand rumours and myths.

If the same standards were applied to the New Testament as are normally applied by historians when assessing the reliability of other allegedly historical texts, it would be regarded as pretty much worthless as a "testament" to anything that really happened.

Comparing the tales of Jesus to the preceding tale of Mithras, it looks like they just cut+paste, then added some stuff in to make it more compelling, a few chinese whispers here and there and bingo! A way to make money.